Method of manufacturing and case hardening gear wheels



Nov'. 30, 1943. G. E. MILLARD A 2,335,295

METHOD OF MANUFACTURING AND CASE 'IARDENIIKzr GEAR WHEELS Filed Dec. 5. 1940 @hij V1/W ATTORNEY f operations.

metre-e Nev. 30,1943

I 2,335,295 MANUFACTURING ANDGASE WHEHS HARDENING GEAR METHOD 0F George n. Minna, seattle, weer. Appueeuen' neeember `s, 1940. seem Ne. asassz avoisine. (ci. 20a-1s) This invention relates tothe vmanufal'icture of.

machine gears. More particularly, ity relates to means utilized in the case hardening of steel gear, wheels; in the steps of a method of case hardening, and in the particular steps `lemployed in the method.

It iswell recognized in the art to which this invention belongs, that machine gears, properly heat treated and case hardened, to increase'. their strength, durability and hardness of wearing surfaces, have many advantages over gears not so treated, Case hardening lis now'common pracsequence of tice, 'and certain methods are welllknown and in e common use wherethe making and cutting .of steel gears are concerned.

The c ase hardening of gear wheels, for various of the gears; for instance, to the teetlfand closely adjacent portions, since the teeth are subjected to thegreatst amount of wear, and'also because it is generally desired that other portions of the gear beworked on by tools of various kind'after the c e hardening operation has been completed; for example, in the preparation of the gear for `mounting oma shaft or for attachment to other parts Therefore, it will be understood particularly by those familiar with the gear cutting art, that it is, undesirable vand impractical to harden those parts quently be nnished or cut. l

'Ihegeneral procedure in the manufacture of of s gear that must subse.

' reasons, is generally conilned to certain portions gears preparatory to case hardening, is to coat the entire gear surface with copper, since a surface while sov coated is not subject to case hardening by the usual heat treatment then to place the gear 'blank in a machine and true up those copper coated portions whereby the-gear blank is to be mounted intm gearcutting machine so that the cutting will vbe accurately done; and, finally, to place the prepared `gear blank in the gear cutting machine and 'cut the teeth therein.- The tooth cutting operation incidentally removes the copper from those particular surfaces that are to bel case hardened, but leaves those parts that are Vnot to be hardened, protectively covered with the copper plating.

. This generally followed method has certain'disadvantages; for example, there is a waste of cop'- per in the coatingof the entire' blank; there extra work required in the truing up of the copper coated mounting portions of the blank preparatory to fixing it`in the gear cutting machine.

and furthermore, there is an unnecessary loss.

of time in the preparatorycoating'and truing e In view of the foregoing disadvantages, and for various otherreasons, it has been the principal object ofthe present invention to provide anovel means for use in the manufacture of machine gears, and a novel method which simpliiles the manufacture and lessens the expense that is usually incident to the case hardening operation. 'l

Other objects of the present invention reside l in the novel form of jig that is provided for use in the manufacture of gears, and in the particular sequence of steps of ,the novel method fol- 'lowed in the case hardening of certain designated portions of gears whereby the manufacture is simplified, and the expense of case hardeningis materially reduced.

In carrying out the above objects of the invention, I have provided the improved -details of construction of a special form of jig, theI preferred formof which is' illustrated in the accompanying drawing, wherein- Fig. 1 isa side view of one form of gear blank as prepared for the formation of a gear therefrom. l

Fig. 2: is a sectional --detail of a formed gear wheel, as applied to the present form of jig, and

' as suspended in a solution for removal, by electrolysis, of copper from parts that are to be case hardened.

Fig. 3 is a sectional detail showing the mannerin which the inner and outer-members of the Jig are fitted to the gear. e

vReferring more in detail to the drawing- I designates what, `for convenience in this description, will bezreferred to as the gear blank.

, This blank has here been illustrated as shaped for the cutting of a bevel d gear wheel, but it is to be understood that t e shape of the gear is of no particular consequence in the present invention, and that it mi ht be a gear wheelji-of any other shape withou .requiring any cliaige in the method and without in any way departing from the spirit of the invention. For ience, inthe mounting of the gear blank in the gear cutting machine. it might, as here shown, .be provided with the hub portion 2 and shank 3 which extend from its opposite faces.

In the present method of manufacture, the gear blank is'rst properly mounted in the gear cutting machine, and the teeth are cut and finished therein.v` Then the gear wheel is removed from the gear cutting machine, and it is copper plated to cutting the teeth. Then, with the plating finished, the gear is applied to a jig, presently to be described in detail, which has for its purpose to cover up those surfaces of the gear that are not to be case hardened. With the gear wheel thus protected by the application of the parts of the jig thereto, it is then immersedl in a suitable solution, for example, a chromic acid, and an electric current so applied that, by the well known action of electrolysis, the copper plating is removed from those surfaces of the gear that are exposed, or outside of the jig. Generally, the parts exposed'are the teeth of the gear and parts closely adjacent thereto; it being understood that the exposed surfaces might be extended as deY sired.

Referring now to Figs. 2 and 3: The surface protecting jig as herein illustrated, comprises a collar or sleeve-like portion 5, adapted to closely fit about the gear hub 2, and' is formed with an annular end flange' or seat 6 adapted to tightly t against the finished outer face of the gear upl to the base of the teeth, or to extend to a greater or lesser extent as desired. Also, ythere is a disk or plate 8, adapted to t tightly against the nished inside face of the gear up to the toothed portion or to a greater or lesser extent as desired. Thus, the parts' 5 and8 p'rotectively overlie those parts of the gear on which it is desired that the copper coating shall remain to prevent these surfaces being case hardened when the gear is given the heat treatment for case hardening the toothed portion.-

The parts 5 and 8 are Aheld securely in place by means of a clamp bracket 9 which is xed pivotally by a bolt I to the sleeve or collar, and at its other end mounts a threaded clamp screw, or the like, I2, adapted to be tightened against the disk 8, thus to hold the parts and 8 sunlciently clamped in place that when immersed in the acid solution, there will be no leakage between the tted surfaces.

Alsothere is a metal handle member I4, xed

to the sleeve 5 and. formedI at its outer end with a Ahook I5 foi` convenience in suspending the parts from the anode terminal I'Ia of the electric circuit used in the process; the circuit being vindicated in Fig. 2, wherein the sourceof electricity is designated at I6, the cathode terminal at I1, and the circuit connections by numerals I8 and I9. A'treatingvessel is designated at 2li-'and the acid solution at 2|.

It win here by mentioned that the jig parts 5, 8 and 9 preferablyA are of aluminum, as this' from the remaining portions particular metal has its advantages when used in the particular solution.

Assuming that a gear blank, prior to any case hardening treatment, has hadl the teeth cut therey in, and has then been copper plated, and has had the parts 5 and 8 of the protecting jig applied thereto as illustrated in Fig. 2, it is quite apparent then that when the parts are immersed in the acid, and connected in the electric circuit, asshown, an electrolytic action will be set up to effectively removethe copper from the exposed portions of the gear. By proper` watching, the gear may be removed at the time when all the exposed. copper has been removed, but before the steel has been acted on. In this connection, it will be stated that the particular acid herein mentioned is very desirable, since it does not readily have any material effect on steel.

With the copper then removed from the parts that are to be case hardened, the' gear is given the usual case hardening heat treatment. After this' has been finished, the copper may be removed ofthe gear by sand blast or otherwise. l

Having thus described my invention, what I claim as new therein and desire to secure by Letters Patent is- 1. The method of manufacturing machine l gears with case hardened teeth, which comprises machining the gear blank to inish the gear and teeth; then electrolytically applying a copper plating to the entire surface ofthe finished gear;- then applying fitted complemental shielding members over the nished gear and leaving the teeth unshielded; then electrolytically removing the copper plating from the unshielded teeth; then removing the shielding members from the gear; then subjecting the gear to case hardening treatment; and then nally removing the remaining copper plating from the gear.

2. The method of manufacturing machine gears with case hardened teeth, which comprises machining the gear blank to finish the gear and teeth; then electrolytically applying a copper in a chromic acid bath the copper plating from the unshielded* teeth; then removing the shielding members from the gear; then subjecting the gear to case hardening treatment; and then finally re- 

